Nginx Fastcgi_cache performance - Disk cached VS tmpfs cached VS serving static file

[ddutra]

Hello guys,

First of all, thanks for nginx. It is very good and easy to setup. And it is
kind of a joy to learn about it.

Two warnings: this performance thing is addictive. Every bit you squeeze,
you want more. And English is my second language so pardon me for any
mistakes.

Anyways I am comparing nginx performance for wordpress websites in different
scenarios and something seems weird. So I am here to share with you guys and
maybe adjust my expectations.

Software                                                                    
       
#       NGINX 1.4.2-1~dotdeb.1                                              
           
#       PHP5-CGI 5.4.20-1~dotdeb.1                                          
           
#       PHP-FPM 5.4.20-1~dotdeb.1                                           
           
#       MYSQL Server 5.5.31+dfsg-0+wheezy1                                  
           
#       MYSQL Tuner 1.2.0-1                                                 
           
#       APC opcode 3.1.13-1 

This is a ec2 small instance. All tests done using SIEGE 40 concurrent
requests for 2 minutes. All tests done from localhost > localhost.

Scenario one - A url cached via fastcgi_cache to TMPFS (MEMORY)
SIEGE -c 40 -b -t120s
'http://www.joaodedeus.com.br/quero-visitar/abadiania-go'

Transactions:                    1403 hits
Availability:                 100.00 %
Elapsed time:                 119.46 secs
Data transferred:              14.80 MB
Response time:                  3.36 secs
Transaction rate:              11.74 trans/sec
Throughput:                     0.12 MB/sec
Concurrency:                   39.42
Successful transactions:        1403
Failed transactions:               0
Longest transaction:            4.43
Shortest transaction:           1.38


Scenario two - Same url cached via fastcgi_cache to disk (ec2 oninstance
storage - ephemeral)

Transactions:                    1407 hits
Availability:                 100.00 %
Elapsed time:                 119.13 secs
Data transferred:              14.84 MB
Response time:                  3.33 secs
Transaction rate:              11.81 trans/sec
Throughput:                     0.12 MB/sec
Concurrency:                   39.34
Successful transactions:        1407
Failed transactions:               0
Longest transaction:            4.40
Shortest transaction:           0.88


Here is where the first question pops in. I dont see a huge difference on
ram to disk. Is that normal? I mean, no huge benefit on using ram cache.

Scenario three - The same page, saved as .html and server by nginx

Transactions:                    1799 hits
Availability:                 100.00 %
Elapsed time:                 120.00 secs
Data transferred:              25.33 MB
Response time:                  2.65 secs
Transaction rate:              14.99 trans/sec
Throughput:                     0.21 MB/sec
Concurrency:                   39.66
Successful transactions:        1799
Failed transactions:               0
Longest transaction:            5.21
Shortest transaction:           1.30


Here is the main question. This is a huge difference. I mean, AFAIK serving
from cache is supposed to be as fast as serving a static .html file, right?
I mean - nginx sees that there is a cache rule for location and sees that
there is a cached version, serves it. Why so much difference?

Cache is working fine
35449 -
10835 HIT
1156 MISS
1074 BYPASS
100 EXPIRED

Any help is welcome.
Best regards.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,243412,243412#msg-243412